In an optoelectronic sensor device which is known from GB-C-1 283 528, the transverse passage of a spun yarn is detected in a ring spinning machine, with the unwinding running yarn orbiting in an opening. The opening has a light beam passing diametrically therethrough, the light beam being emitted from a light source, which is arranged in an opening wall, and through the opening onto an opposite receiver. A slit aperture is arranged in front of the receiver. The receiver responds to light variations or to the shadow of the yarn which passes over the slit aperture. Disturbing factors, such as vibrations, extraneous light, or the like, can prompt the receiver to output a wrong signal, despite the fact that the yarn has not properly passed through the slit aperture in the scanning zone.
In weft-yarn measuring and storing devices, as typically used on weft looms for providing weft yarn, exact information as to when and that the weft yarn passes through a scanning zone upon withdrawal is required for controlling and monitoring the feed operation of each weft yarn. To this end, at least one withdrawal sensor is provided which is equipped with a receiver that is oriented towards the illuminated scanning zone and is responsive to light variations. Since vibrations, the effect of extraneous light, or other unwanted factors that are observed during practical operation also prompt the receiver to respond, the significance of the signals gained from the weft-yarn passages is not to be relied on. Therefore, a method has been adopted in practice in which two receivers which are closely arranged one after the other in the axial direction of the storage body are oriented towards the same scanning zone and in which a significant signal for the yarn passage is derived from the response of the two receivers in a differential circuit, the signal being distinguishable from signals produced by unwanted factors because of the fact that an unwanted factor is observed on both receivers at the same time and in the same manner, whereas the yarn is recorded by the two receivers such that the record is offset in time. Nevertheless, this known scanning sensor with the two receivers does not reliably operate for several reasons. The receiving surface of each receiver is approximately circular as a rule. The yarn which moves relative to the receiving surface is only gradually imaged by its reflective light or its shadow because of the circular form of the receiving surface and due to transitional imaging. In addition, the response sensitivity of the receiver in the edge portions of the receiving surface is weaker than near the center. The signal which is evaluated in the differential circuit is therefore weak because of the gradual signal increase and the also gradual signal decrease and requires considerable amplification efforts which, however, are undesirable in the case of unwanted factors. Furthermore, such measuring and storing devices imperatively operate with a distinctly axial reciprocating movement of the yarn supply border at the withdrawal side of the yarn supply on the storage body, especially with when yarn separation and/or when a lively pattern is being weaved. This results in a yarn withdrawal geometry in which yarn withdrawn from the last winding of the yarn supply varies its longitudinal orientation in the scanning zone between approximately axial and approximately circumferential, respectively related to the axis of the storage body. With an approximately axial orientation of the yarn in the scanning zone the yarn is perceived by both receivers at the same time and in a similar manner, which renders a distinction difficult, or even excludes it, with respect to unwanted factors that are also perceived at the two receivers at the same time and in a similar manner.
It is the object of the present invention to provide a simple optoelectronic sensor device of the above-mentioned type and a weft-yarn measuring and storing device in which a strong and significant useful signal which can easily be distinguished from signals caused by unwanted factors can be produced on the basis of the yarn passing therethrough. In the measuring and storing device, the withdrawal sensor is intended to supply exact information as to when and that the yarn has passed through the scanning zone, despite varying yarn withdrawal speeds, different yarn qualities and variations of the orientation of the yarn in the scanning zone. The term "yarn" generally refers to yarn-like substrates, such as threads, twisted threads, filaments, spun threads, wires, narrow bands, foil-slips, or the like.
However, complicated electronic sensor devices whose receivers image or sharply image the object to be scanned and require position-sensitive detectors, optical imaging systems and high-quality circuits are explicitly excluded. Such sensor devices are too complicated and expensive for scanning a yarn passing therethrough either as such or in a measuring and storing device and are thus excluded from use for other reasons as well (for instance WO 89/00215, EP-A-0529 281).
The above object is achieved in an optoelectronic sensor device wherein first and second slit apertures are arranged relative to each other at an angle of 90.degree. or less, and in a weft-yarn measuring and storing device having such an optoelectronic sensor device.
In the optoelectronic sensor device and in the weft-yarn measuring and storing device, an exact, significant and strong useful signal which can easily be distinguished from signals resulting from unwanted factors is obtained during scanning of each yarn passage as a special advantage, i.e., under efforts which are small under constructional and circuitry aspects and are not costly. The orientation of the yarn direction in the scanning zone is of no importance any more, since the yarn passes through the two slit apertures at different times or with different geometrical location, so that the differential evaluation of the response of the two receivers leads, at any rate, to a clear signal which clearly differs from a signal resulting from an unwanted factor, because the unwanted factor is recorded at the two receivers at the same time and with the same geometrical location. Furthermore, a strong modulation of the signal is obtained on the basis of the yarn passage in the scanning zone because, on the one hand, the less sensitive edge portions of the receiving surfaces are covered and do not become operative and because, on the other hand, the yarn becomes visible in its full size at an extremely rapid pace (almost no transition) in each slit aperture (by its reflective light or its shadow). Since the time which passes up to a full imaging of the yarn onto the receiving surface portion narrowed by the slit aperture is extremely short, as is also the time up to a complete disappearance of the full image, the signal which is produced by a differential evaluation technique contains strong frequency portions which can be derived with little amplification efforts and which are not present in a signal produced by an unwanted factor. On the whole, the use of two receivers, two slit apertures and the geometrical arrangement of the slit apertures independently of the orientation of the yarn in the scanning zone, the strength and frequency of unwanted factors, and also largely independently of contaminations, results in a strong and significant signal obtained on the basis of a yarn passage, which can be further processed by taking little circuitry efforts. Use is made of simple and inexpensive receivers which respond to light variations. The response characteristics of these receivers, which are smooth as such, are respectively enhanced in an unexpected manner by the slit aperture during proper yarn passage. The receivers can be arranged in close relationship with one another. This advantageous result is guaranteed even at maximum yarn speeds which are customary in modern yarn-processing systems. However, it is also possible to use more than two receivers each with one respective slit aperture.
The edge portions of the receiving surface which are critical with respect to the response characteristics of receivers reacting to light variations preferably define a diameter greater than the slot aperature; However, it is also possible to make the slit aperture as long as or even longer than the diameter of the receiving surface.
In the embodiment wherein the receivers are jointly connected to an evaluation circuit the useful signal is produced from the response of the two receivers in the evaluation circuit which is designed as a differential circuit.
In the embodiment wherein one slit aperature extends in a circumferential direction of the storage drum and another slot aperature extends in an axial direction; a compact construction of the withdrawal sensor can be achieved, with the withdrawal sensor being virtually independent of the speed variations of the yarn moving through the scanning zone, and being above all independent of the respective orientation of the yarn in the scanning zone.
The embodiment wherein an imaginary extension of one slit aperatur intersects another slit aperature is especially expedient. It is thereby ensured that the yarn is perceived by both receivers only on portions of the receiving surfaces which are limited by the slit apertures, and independently of the orientation of the yarn in the scanning zone at different times and/or with different geometries.
An especially expedient embodiment has the slit apertures arranged in a T; A situation is here expedient where the transverse bar T is slightly spaced apart from the upright leg, resulting in an asymmetry during scanning of the yarn through the geometrical configuration of the slit aperture, the asymmetry being important for a distinction between useful signal and unwanted signal and for a strong useful signal.
The shapes of the slit apertures can be rectangular, double-concave or double-convex, and ensure that a full light impingement or shadowing of the portions of the receiving surface begins and stops, respectively, at a very rapid pace to achieve a frequency portion which is as high as possible for the useful signal.
Slit apertures of the same size are advantageous.
The embodiment wherein the slit apertures are arranged such that a movement of a yarn over the slit aperatures which is geometrically identical or in time is prevented. is especially important. Such an adaptation of the positions of the slit apertures to possible orientations of the yarn in the scanning zone rules out a situation where the yarn is perceived by the two receivers with the same geometry or at the same time.
The embodiment block-shaped holder with channels permits a compact, operationally safe and also reliable design of the withdrawal sensor. The holder with its channels, the receivers, the light source and the slit apertures is a component which is simple and inexpensive and which can be prefabricated with high accuracy and can advantageously be accommodated and easily replaced even within a limited space.
In the embodiment the channels are arranged in specific inclinations. the components are combined within a very confined constructional space.
In the embodiment wherein a transparent cover pane is provided on the holder the cover pane protects the components arranged in the holder from soiling or dust.
The slit apertures may be spaced apart in an axial direction of the storage body at a dimensional distance of approximately the width of the slit apertures. This dimensional distance has turned out to be advantageous.
Finally, in the embodiment wherein the slit apertures are formed in a plate which may be adjusted in position the respective position of the slit apertures and the relative position between the slit apertures can be set or adjusted.